Fig. 3A: Portable chest shows subtle contour abnormality
of the right side of the mediastinum (curved arrow) and
evidence of bilateral AVN of the shoulders (straight arrows).
Fig. 3A: Portable chest shows subtle contour abnormality
of the right side of the mediastinum (curved arrow) and
evidence of bilateral AVN of the shoulders (straight arrows).
Fig. 3D: Posterior image from a Tc99m-WBC scan
shows intense uptake in the posterior mediastinal mass.
Ask-Upmark first described a patient with extramedullary hematopoiesis in 1945.[2] Extramedullary hematopoiesis is seen in a variety of disorders including thalassemia, a variety of hemolytic anemias, lymphoma/leukemia, hyperparathyroidism and chronic pneumonia. It can involve a number of organ systems, and reports describe involvement of the thorax, liver, spleen, skin, and adrenal glands [3]. While it is often clinically silent, there are numerous case reports describing cord compression secondary to posterior mediastinal involvement.[1] While the pathogenesis of EMH remains obscure, findings of hematopoietic cells in the pulmonary vessels suggest an embolic source, probably from the spleen.[4] Other theories postulate direct extension of hematopoietic cells from expansion and extension from adjacent ribs and vertebral bodies in these patients.[2] While historically these masses were often resected or treated with radiation, these masses are currently simply observed if they are not clinically symptomatic.
Radiologically, bilateral smoothly marginated masses in the thorax have been classically described as demonstrated in the case presented here (See Fig. 3 on this page). These masses contain fat and are almost always situated between the T8 and T12 vertebral bodies.[5] Other rare manifestations in the thorax include interstitial infiltrates and ground glass opacities felt to be secondary to diffuse infiltration by hematopoietic cells.[6] Pleural effusions are reported but rare, and large spontaneous hemothoraxes have also been described.[5] Gumbs et al described eight cases of EMH in patients with sickle cell disease. Similar to our patient, the disease was unilateral in 7 of 8 patients and the masses range in size from 0.5 to 7 cm. CT scans performed in 3 of these patients showed homogenous soft tissue masses which did not change on subsequent CT scans. [7]. Our patient, unlike those in the Gumbs series, did show significant vertebral body erosion. In one patient with EMH, fatty replacement of the mass was seen following the patient’s splenectomy.[8] If confirmation of EMH is needed, correlation with Tc99m sulfur colloid or 99mTc-WBC can be performed. Biopsy should be avoided, as excessive bleeding can occur.
References:
1. Armstrong P. Mediastinal and Hilar Disorders. In: Armstrong P, Wilson AG, Dee P, Hansel DM.
Imaging of Diseases of the Chest. Mosby, St. Louis, 1995;780.
2. Ask-Upmark E. Tumor simulated intrathoracic heterotopias of
bone marrow. ACTA Radiol 1945;No.26:425-439.
3. Ross P, Logan W. Roentgen Findings in extramedullary hematopoiesis.
AJR 1969;106:604-613.
4. Cohen SM. Bone marrow in veins. JAMA 1925;11:732-733.
5. Shaver RW. Extramedullary hematopoiesis in myeloid metaplasia.
AJR 196;. 137:874-876.
6. Case Records of Massachusetts General Hospital, Case 14,1968.
New England J Med 1968; 278:782-791.
7. Gumbs R, Higgenbotham-Ford et al. Thoracic extramedullary hematopoiesis
in sickle cell disease. AJR 149:889-893.
8. Wright SH Fishman EK Diffuse pulmonary extramedullary hematopoieses
in a patient with myelofibrosis:CT findings. JCAT 1994; 18(5):815-817.
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